Modern manufacturing equipment is capable of producing products at very high speeds. For example, it is not at all uncommon for modern cigarette making equipment to produce cigarettes at the rate of 5000-6000 per minute, and speeds as high as 12,000 per minute are also achievable. It is, of course, desirable to inspect the appearance of products to the greatest possible extent. Abnormal appearance in itself may be a reason for rejecting a product. Moreover, abnormal appearance may indicate an underlying structural defect which may be another reason why the product should be rejected. In addition to facilitating rejection of defective products, appearance inspection may be used to identify what types of defects might be occurring so that the production equipment can be adjusted to reduce the occurrence of such defects.
In general, a more complete the inspection of products is preferred, including, if possible, an inspection of the full image of to each product, rather than just an inspection of portions of each image or an inspection of only a presumably representative sample of product images. Also, the more current the results of the inspection the better, so that when a succession of defective products is detected, prompt corrective action can be undertaken to minimize the production of products with the defect.
The foregoing considerations become compounded and more critical at elevated production speeds, where high speed equipment tends to be more sensitive to misadjustments, poor maintenance and/or improper operation. The need for immediate detection of defects is also more critical with high speed equipment, because massive quantities of defective products can be produced in just a short time. Defects must be detected promptly, and the equipment either stopped or adjusted to eliminate the cause of the defects.
During the manufacture of cigarettes, various types of defects may appear at their circular end face of the filter or at other substantially circular surfaces.
Although most cigarettes are circular in cross-section, some cigarettes are oval. It will be readily apparent to those skilled in the art how the principles of the present invention can be adapted to oval cigarettes. Because oval objects are sufficiently like circular objects for purposes of the present invention, all such objects will be referred to herein as circular or substantially circular.
Among the defects which might appear at the circular end surfaces of cigarettes are the following: (1) an absence of a intended component such as a filter; (2) an improper size (i.e., it is either too large or too small); (3) an improper shape (e.g., not sufficiently circular); (4) an improper sealing of a wrapper (e.g., a "flag" appears on the plug wrap (the paper wrapper around a filter component) or a "flag" appears on the tipping paper (the wrapper which joins the filter to the tobacco rod)); (5) a gap appears between the plug wrap and the underlying filter material (a so-called "by-pass") or between the tipping paper and the underlying filter plug (another form of by-pass); or (6) a discoloration at the filter end surface (e.g., in the case of charcoal filters, when one or more particles of charcoal has located on the end surface of the filter (so-called "black eyes")).
In view of the foregoing, it is an object of the present invention to provide methods and apparatus for inspecting the appearance of substantially circular objects such as the ends of cigarettes for one or more defects of the type described above.
It is another object of this invention to provide methods and apparatus for inspecting the appearance of substantially circular objects such as the ends of cigarettes at the extremely high speeds at which such articles are typically made in modern manufacturing equipment.